There is a growing national need for a system capable of detecting small amounts of radioactive material, such as special nuclear material (SNM) and shielded highly enriched uranium (HEU), especially in an unknown environment and an unknown shielding scenario such as within a large metropolitan region. Upon detection in such a scenario, the unknown radioactive material must be identified, such as by its spectral signature. Additionally, a detection device having the ability to switch modes between low count rate detection (background radiation), small source detection, and high count rate is required, especially in consequence management situations where the count rate is high enough to present an immediate indication of significant amounts of nuclear material or a dangerous radiation environment.
In the past, various types of radiation detectors in various packages have been utilized, such as scintillation-based field detectors and cryogenically cooled high resolution germanium and silicon detectors. One problem with scintillation detectors, however, is that they do not provide high spectral resolution. And cryogenically cooled detectors require large batteries, external power, or cryogens to maintain operating temperature. Due to these problems, scintillation and cryogenically cooled detectors have been difficult to use in the field in a compact, handheld battery powered unit that provides in situ diagnostics.